When i filed my tax return for 2021 I used a cd download. my computer crashed and i was not able to recover it. how can I recover my 2021 tax return with turbo tax?

Sorry, If you used the Desktop CD/Download program then the only copy is on your computer and not saved or stored online. So you need to make and keep your own backups.

Or request a transcript from the IRS
https://www.irs.gov/individuals/get-transcript

Or get a copy of your return using form 4506
https://www.irs.gov/pub/irs-pdf/f4506.pdf

If you used desktop software downloaded/installed from a CD to your own computer, then the tax files are stored locally on your own hard drive or any backup device you used like a flash drive.  They are not stored online.  If you cannot recover them due to a hard drive failure, etc. you can get a free transcript from the IRS or for a fee of $43, an actual copy of your tax return.

https://www.irs.gov/individuals/get-transcript

https://www.irs.gov/pub/irs-pdf/f4506.pdf